Method of manufacturing a composite filter media

ABSTRACT

A method of making a composite filter media includes, in an exemplary embodiment, forming a nonwoven fabric mat that includes a plurality of synthetic fibers by a spunbond process, and calendaring the nonwoven fabric mat with embossing calendar rolls to form a bond area pattern comprising a plurality of substantially parallel discontinuous lines of bond area to bond the synthetic fibers together to form a nonwoven fabric, the nonwoven fabric having a minimum filtration efficiency of about 50%, measured in accordance with ASHRAE 52.2-1999 test procedure. The method also includes applying a nanofiber layer by electro-blown spinning a polymer solution to form a plurality of nanofibers on at least one side of the nonwoven fabric mat to form the composite filter media, the composite filter media having a minimum filtration efficiency of about 75%, measured in accordance with ASHRAE 52.2-1999 test procedure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/843,228, filed Aug. 22, 2007, which claims priority toProvisional Patent Application Ser. No. 60/893,008, filed Mar. 5, 2007.

BACKGROUND OF THE INVENTION

The field of the invention relates generally to a composite nonwovenfilter media, and more particularly, to a spunbond nonwoven filter mediahaving a nanofiber based layer applied to at least one surface.

Some known filter media composite constructs incorporate a wet-laidpaper making process to produce the substrate, and an electro-spuntechnology to deposit a lightweight nanofiber coating on one or bothsides of the filter media substrate. Typically the media substrate has abasis weight of 100-120 grams per square meter (g/m²), and the nanofiberlayer has a basis weight of 0.1 g/m² or less.

It is known that the lightweight nanofiber layer is vulnerable to damagein high mechanical stress applications, especially because the nanofiberlayer is formed from fibers with diameters less than 500 nanometer (nm),and more typically, 100 nm. It is known that there are “shedding”problems where the nanofibers are shed from the filter media because ofrelatively weak attraction bonds between the nanofibers and the basemedia for conventional electro-spun fibers that rely on polarityattraction forces. Also, known electro-spun nanofiber layers are twodimensional in structure or a single fiber layer in thickness, and whenthe nanofiber layer cracks or breaks, dust can readily penetrate thebase media substrate After the nanofiber layer is damaged, dust ispermitted to penetrate the base media and contribute to a rise in theoperating pressure drop of the filter. Further, known media substratesalso have mechanical stress limitations and are prone to deformationunder high dust loading.

These known filter media composite constructs when used to filter inletair of power generation gas turbines can permit fine dust particulatesto penetrate the filter over the operating life of the filter.Typically, this known filter media type will have a new or cleanoperating electrically neutral efficiency providing for around 55% ofcapture of 0.4 μm particles, at a pressure drop typically greater than7.0 mm H₂O, and a Quality Factor less than 300, when tested inaccordance with the ASHRAE 52.2-1999 test procedure at the knownoperating flow rate. It is known that as much as 15 to 20 pounds of dustcan penetrate known filter media over a 24,000 hour operating lifebecause of this low initial efficiency. Exposing the turbine blades todust over an extended time can cause serious and catastrophic foulingand erosion of the turbine blades. The current procedure of cleaning theturbine blades requires taking the turbine off-line at periodicintervals to water wash the blades clean. Turbine down time is expensivebecause the turbine is not operating and therefore, power generation iscurtailed. It would be desirable to provide a higher efficiency filtermedia than the known filter media at a similar or reduced pressure dropto reduce or eliminate turbine down time to clean the turbine bladesand/or the replacement of damaged blades.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method of making a composite filter media is provided.The method includes forming a nonwoven fabric mat that includes aplurality of synthetic fibers by a spunbond process, and calendaring thenonwoven fabric mat with embossing calendar rolls to form a bond areapattern comprising a plurality of substantially parallel discontinuouslines of bond area to bond the synthetic fibers together to form anonwoven fabric, the nonwoven fabric having a minimum filtrationefficiency of about 50%, measured in accordance with ASHRAE 52.2-1999test procedure. The method also includes applying a nanofiber layer byelectro-blown spinning a polymer solution to form a plurality ofnanofibers on at least one side of the nonwoven fabric mat to form thecomposite filter media, the composite filter media having a minimumfiltration efficiency of about 75%, measured in accordance with ASHRAE52.2-1999 test procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is cross sectional illustration of an exemplary embodiment of acomposite filter media.

FIG. 2 is a photomicrograph of the bicomponent fibers shown in FIG. 1.

FIG. 3 is a photomicrograph of the base media substrate shown in FIG. 1.

FIG. 4 is a top illustration of the bond pattern of the base mediasubstrate shown in FIG. 1

FIG. 5 is a side illustration of a filter cartridge that includes thefilter media shown in FIG. 1.

FIG. 6 is a perspective illustration of a filter assembly that includesthe filter cartridge shown in FIG. 4.

FIG. 7 is a graph of fractional efficiency versus particle size of basemedia substrates at various basis weights in accordance with anexemplary embodiment.

FIG. 8 is a graph of fractional efficiency versus particle size of basemedia substrates with and without a nanofiber layer in accordance withan exemplary embodiment compared to a comparative base media substratewith and without a nanofiber layer.

FIG. 9 is a bar graph of pressure drop versus base media substrate withand without a nanofiber layer in accordance with an exemplary aspectcompared to a comparative base media substrate with and without ananofiber layer.

DETAILED DESCRIPTION OF THE INVENTION

A composite filter media for filter assemblies is described in detailbelow. In an exemplary embodiment, the composite filter media includes amedia substrate of a synthetic nonwoven fabric that is formed frombicomponent fibers by a unique spunbond process. A nanofiber layer isdeposited on at least one side of the media substrate. The compositemedia provides an initial filtration efficiency of about 75% or greaterretained capture of 0.4 μm particles, when tested in accordance with theAmerican Society of Heating, Refrigerating and Air-ConditioningEngineers (ASHRAE) 52.2-1999 test procedure, which is about a 20%increase in performance compared to known filter media. In addition, thecomposite media provides the 75% efficiency at a greater than 30% lowerpressure drop than known filter media. The composite filter media ismore durable than known filter media and provides for lower pressuredrop build-up because of less deflection of the filter media from theforces exerted on the filter media during the filtering and reversecleaning operations. The composite filter media may have a qualityfactor (Q_(f)) of greater than about 450, and in another embodiment,greater than about 500. Also, the composite filter media may have aresistance (or pressure drop) of less than 4.0 mm water, measured inaccordance with EN-1822 (1998), with the base media substrate having aresistance of less than about 2.5 mm water, measured in accordance withEN-1822 (1998). Further, the spunbond media substrate is more efficientthan known filter media substrates at an equivalent or lower pressuredrop. The bicomponent fibers used to form the media substrate are finerthan fibers used to form known filter media. Further, the nanofibermembrane layer has a higher basis weight than known filter media whichpermits the filter media to clean down more effectively under reversepulse cleaning than known filter media. The high basis weight of thenanofiber layer provides for a durable three dimensional surfacefiltration layer which has an extensive tortuous path that permits highefficiency and fine particle capture without substantially restrictingair flow or increasing pressure drop.

By “quality factor (Q_(f))” is meant the parameter defined by theequation:

Q _(f)=−25000·log(P/100)/Δp

Where “P”=particle penetration in % and “Δp”=pressure drop across themedia in Pascals.

By “resistance” is meant the resistance (pressure drop) as measuredusing the test method described in EN 1822 (1998).

Referring to the drawings, FIG. 1 is a sectional illustration of anexemplary embodiment of a filter media 10. Filter media 10 includes abase media substrate 12 having a first side 14 and a second side 16. Ananofiber layer 20 is deposited onto first side 14 of media substrate.In another embodiment, nanofiber layer 20 is deposited onto second side16, and in another embodiment, nanofiber layer 20 is deposited on eachof first and second sides 14 and 16.

Media substrate 12 is a nonwoven fabric formed from syntheticbicomponent fibers using a spunbond process. The nonwoven fabricincludes bicomponent fibers having a thermoplastic fiber component addedto the nonwoven fabric during its production. Suitable bicomponentfibers are fibers having a core-sheath structure, an island structure ora side-by-side structure. Referring also to FIG. 2, in the exemplaryembodiment, a bicomponent fiber 30 includes a core 32 and a sheath 34circumferentially surrounding core 32. Bicomponent fibers 30 aremeltspun through jets into a plurality of continuous fibers which areuniformly deposited into a random three dimensional web. The web is thenheated and embossed calendered which thermally bonds the web into aconsolidated spunbond fabric 36, shown in FIG. 3. Heat from contact ofthe calendar roll embossing pattern softens or melts the thermoplasticsheath 34 of bicomponent fibers 30 which binds the nonwoven fiberstogether at the contact points of calendar roll embossing pattern. Thetemperature is selected so that at least softening or fusing of thelower melting point sheath 34 portion of bicomponent fibers 30 occurs.In one embodiment, the temperature is about 90° C. to about 240° C. Thedesired connection of the fibers is caused by the melting andre-solidification of sheath portion 34 after cooling.

Bicomponent fibers 30 have diameter of about 12 microns to about 18microns which is finer than the known fibers used in traditional andcommon spunbond products. A unique aspect of base media substrate 12 isthe bond pattern used to consolidate spunbond base media 12. The bondpattern is defined by the embossing pattern of the calendar rolls.Traditional spunbond media used in filtration have a bond area (landarea) of around 19 to 24 percent. The bond area provides for mediadurability and function while at the same time the bond points createareas of fused polymer that have zero air flow.

Referring also to FIG. 4, a bond pattern 40 on base media 12 attains anacceptable durability to base media 12, while allowing more fiber to beavailable for filtration thus increasing filtration efficiency. Bondpattern 40 includes a plurality of parallel discontinuous lines 42 ofbond area extending across base media 12. The parallel discontinuouslines 42 of bond area are off-set from each other so that at a locationof no bond area 44 in a discontinuous line 42 is aligned with a bondarea 46 of an adjacent discontinuous line 42. The bond area 46 ofspunbond bicomponent fibers 30 in media 12 is about 10 percent to about16 percent of the total area of the fabric as compared to the bond areaof about 19 to 24 percent of known spunbond fabrics. The lower bondareas allow for base media 12 to have increase air permeability orinversely low pressure drop when tested at a given air flow. In theexemplary embodiment the basis weight of base media 12 is about 100 g/m²to about 330 g/m², in another embodiment, about 150 g/m² to about 220g/m²

Any suitable synthetic bicomponent fiber 30 can be used to make thenonwoven fabric of media substrate 12. Suitable materials for core 32and sheath 34 of bicomponent fiber 30 include, but are not limited to,polyester, polyamide, polyolefin, thermoplastic polyurethane,polyetherimide, polyphenyl ether, polyphenylene sulfide, polysulfone,aramid, and mixtures thereof. Suitable materials for the sheath of thebicomponent fiber include thermoplastic materials that have a lowermelting point than the material of the core of the bi-component fiber,for example polyester, polyamide, polyolefin, thermoplasticpolyurethane, polyetherimide, polyphenyl ether, polyphenylene sulfide,polysulfone, aramid, and mixtures thereof.

In the exemplary embodiment, nanofiber layer 20 is formed by anelectro-blown spinning process that includes feeding a polymer solutioninto a spinning nozzle, applying a high voltage to the spinning nozzle,and discharging the polymer solution through the spinning nozzle whileinjecting compressed air into the lower end of the spinning nozzle. Theapplied high voltage ranges from about 1 kV to about 300 kV. Theelectro-blown spinning process of forming nanofibers and the uniqueapparatus used is described in detail in U.S. Patent ApplicationPublication No. 2005/00677332. The electro-blown spinning processprovides a durable three dimensional filtration layer of nanofibers thatis thicker than known nanofiber filtration layers on known filter media.In the exemplary embodiment the basis weight of nanofiber layer 20 isabout 0.6 g/m² to about 20 g/m², in another embodiment, about 2 g/m² toabout 20 g/m², in another embodiment, about 5 g/m² to about 10 g/m², inanother embodiment, about 1.5 g/m² to about 2.5 g/m². The nanofibers innanofiber layer 20 have an average diameter of about 500 nm or less.

In alternate embodiments, nanofiber layer 20 may be formed byelectrospinning, centrifugal spinning, or melt blowing. Classicalelectrospinning is a technique described in detail in U.S. Pat. No.4,127,706. A high voltage is applied to a polymer in solution to createnanofibers and nonwoven mats. However, total throughput inelectrospinning processes is too low to be viable in forming heavierbasis weight webs. Centrifugal spinning is a fiber forming process thatincludes supplying a spinning solution having at least one polymerdissolved in at least one solvent to a rotary sprayer having a rotatingconical nozzle. The nozzle has a concave inner surface and a forwardsurface discharge edge. The spinning solution moves through the rotarysprayer along the concave inner surface so as to distribute the spinningsolution toward the forward surface of the discharge edge of the nozzle.Separate fibrous streams are formed from the spinning solution while thesolvent vaporizes to produce polymeric fibers in the presence or absenceof an electrical field. A shaping fluid can flow around the nozzle todirect the spinning solution away from the rotary sprayer. The fibersare collected onto a collector to form a nanofiber web. In addition,melt blowing is described in detail in U.S. Pat. No. 6,520,425.

Media substrate 12 has a high air permeability compared to known filtermedia which permits improved mechanical adhesion of the nanofibers tomedia substrate 12. As nanofiber layer 20 is applied to first side 14 ofmedia substrate 12, a vacuum may be applied from second side 16 of mediasubstrate during the electro-blown spinning process to hold thenanofibers on the substrate. In combination with the drying temperaturesused in the application of nanofiber layer 12, softening of sheathportion 34 of bicomponent fiber 30 occurs and nanofiber layer 20 isfurther densified and bonded to spunbond base media substrate 12. Incombination with the high air permeability of media substrate 12, theeffectiveness of the vacuum becomes more effective which provides for astrong mechanical bond of the nanofibers to the bicomponent fibers ofmedia substrate 12.

Suitable polymers for forming nanofibers by the electro-blown spinningprocess are not restricted to thermoplastic polymers, and may includethermosetting polymers. Suitable polymers include, but are not limitedto, polyimides, polyamides (nylon), polyaramides, polybenzimidazoles,polyetherimides, polyacrylonitriles, polyethylene terephthalate,polypropylene, polyanilines, polyethylene oxides, polyethylenenaphthalates, polybutylene terephthalate, styrene butadiene rubber,polystyrene, polyvinyl chloride, polyvinyl alcohol, polyvinylidenechloride, polyvinyl butylene, polyacetal, polyamide, polyester,polyolefins, cellulose ether and ester, polyalkylene sulfide,polyarylene oxide, polysulfone, modified polysulfone polymers, andmixtures thereof. Also, materials that fall within the generic classesof poly (vinylchloride), polymethylmethacrylate (and other acrylicresins), polystyrene, and copolymers thereof (including ABA type blockcopolymers), poly (vinylidene fluoride), poly (vinylidene chloride),polyvinylalcohol in various degrees of hydrolysis (87% to 99.5%) incrosslinked and non-crosslinked forms may be used and copolymer orderivative compounds thereof. One suitable class of polyamidecondensation polymers are nylon materials, such as nylon-6, nylon-6, 6,nylon 6, 6-6, 10, and the like. The polymer solution is prepared byselecting a solvent that dissolves the selected polymers. The polymersolution can be mixed with additives, for example, plasticizers,ultraviolet ray stabilizers, crosslink agents, curing agents, reactioninitiators, and the like. Although dissolving the polymers may notrequire any specific temperature ranges, heating may be needed forassisting the dissolution reaction.

It can be advantageous to add plasticizers to the various polymersdescribed above, in order to reduce the T_(g) of the fiber polymer.Suitable plasticizers will depend upon the polymer, as well as upon theparticular end use of the nanofiber layer. For example, nylon polymerscan be plasticized with water or even residual solvent remaining fromthe electrospinning or electro-blown spinning process. Otherplasticizers which can be useful in lowering polymer T_(g) include, butare not limited to, aliphatic glycols, aromatic sulphanomides, phthalateesters, including but not limited to, dibutyl phthalate, dihexylphthalate, dicyclohexyl phthalate, dioctyl phthalate, diisodecylphthalate, diundecyl phthalate, didodecanyl phthalate, and diphenylphthalate, and the like.

FIG. 5 is a side illustration of a filter element 50 formed from filtermedia 10. In the exemplary embodiment, filter media 10 includes aplurality of pleats 52. Filter element 50 includes a first end cap 54and an opposing second end cap 56 with filter media 10 extending betweenend caps 54 and 56. Filter element 50 has a tubular shape with aninterior conduit 58 (shown in FIG. 6). Filter element 50 is cylindricalin shape, but can also be conical as shown in FIG. 6. Filter element 50can also include an inner and/or an outer support liner to providestructural integrity of filter element 50 and/or support for filtermedia 10.

FIG. 6 is a perspective illustration of a filter assembly 60 thatincludes a plurality of filter elements 50 mounted to a tube sheet 62 inpairs in an end to end relationship. Tube sheet 62 separates the dirtyair side from the clean air side of filter assembly 60. A cleaningsystem 64 for cleaning filter elements 50 with pulsed air includes aplurality of air nozzles 66 mounted to air supply pipes 68. Pulses ofcompressed air directed into interior conduit 58 of filter elements 50are used to clean filter elements 50 of collected dirt and dust.

Flat sheets of base media substrate 12 test samples having various basisweights were compared to a comparative base media substrate in a flatsheet fractional efficiency test in accordance with ASHRAE 52.2-1999test method. Air containing KCl particles was directed through each testsample at a flow rate of about 10 ft/min. FIG. 7 shows a graphicalrepresentation of the comparison test and the enhanced filtrationefficiency performance of spunbond base media 12. Line 100 representsbase substrate 12 at a basis weight of 150 g/m², line 102 representsbase substrate 12 at a basis weight of 200 g/m², and line 104 representsbase substrate 12 at a basis weight of 260 g/m². Line 106 represents acomparative base media substrate. The base media substrates did notinclude a nanofiber layer. Base media substrate 12 at each basis weighthas a higher efficiency than the comparative base substrate over theentire range of particle sizes of the KCl particles.

Flat sheets of base media substrate 12, and base media substrate 12including nanofiber layer 20 were compared to a comparative base mediasubstrate with and without a nanofiber layer in a flat sheet fractionalefficiency test in accordance with ASHRAE 52.2-1999 test method. Aircontaining KCl particles was directed through each test sample at a flowrate of about 10 ft/min. FIG. 8 shows a graphical representation of thecomparison test. Line 110 represents base media substrate 12 at 150g/m², and line 112 represents base media substrate 12 at 150 g/m²,including nanofiber layer 20. Line 114 represents a comparative basemedia substrate and line 116 represents the comparative base mediasubstrate including a nanofiber layer. Base media substrate 12 with andwithout nanofiber layer 20 had a higher efficiency than the comparativebase substrate with and without a nanofiber layer over the entire rangeof particle sizes of the KCl particles.

Flat sheets of base media substrate 12, and base media substrate 12including nanofiber layer 20 were compared to a comparative base mediasubstrate with and without a nanofiber layer in a flat sheet pressuredrop test in accordance with ASHRAE 52.2-1999 test method. Aircontaining KCl particles was directed through each test sample at a flowrate of about 10 ft/min. FIG. 9 shows a graphical representation of thecomparison test. Bar A represents a comparative base media substrate andbar B represents the comparative base media substrate including ananofiber layer. Bar C represents base media substrate 12 at 150 g/m²,and bar D represents base media substrate 12 at 150 g/m², includingnanofiber layer 20. Base media substrate 12 with and without nanofiberlayer 20 had a lower pressure drop than the comparative base substratewith and without a nanofiber layer.

The above described filter elements 50 formed from filter media 10 canbe used for filtering an air stream in almost any application, forexample, for filtering gas turbine inlet air. The unique construction offilter media 10 is more durable than known filter media and provides forrelatively lower pressure drop build-up because of less deflection fromthe forces exerted on the filter media during the filtering and reversecleaning operations. Filter elements 50 can produce an averageefficiency greater than about 75% capture of the most penetratingparticle size of aerosol or dust (about 0.3 to about 0.4 micron) ascompared to an efficiency of about 50-55% of known filter elements.Also, nanofiber layer 20 has a higher basis weight than known filtermedia which permits filter media 10 to clean down more effectively underreverse pulse cleaning than known filter media. Further, the high basisweight of nanofiber layer 20 provides for a durable three dimensionalsurface filtration layer which has an extensive tortuous path thatpermits high efficiency and fine particle capture without restrictingair flow or increasing pressure drop.

The example filter media of Examples 1-4 and Comparative Examples 5-9illustrate a comparison of embodiments of filter media 10 with knownfilter media. Efficiency, resistance and quality factor were measuredfor each filter media of Examples 1-4 and Comparative Examples 5-9.Efficiency was measured in accordance with ASHRAE 52.2-1999 testprocedure, resistance was measured in accordance with EN-1822 (1998),and quality factor Q_(f) was calculated as described above.

Example 1 is a spunbond polyester bicomponent fiber base mediasubstrate, and Example 2 is the base media substrate of Example 1 plus a2 g/m² nanofiber layer formed by an electro-blown spinning process.Comparative Example 3 is a known drylaid polyester base media substrate,and Comparative Example 4 is the known dry-laid polyester base mediasubstrate of Comparative Example 3 plus a 2 g/m² nanofiber layer.Comparative Example 5 is a wet-laid synthetic paper plus a <0.5 g/mnanofiber layer. Comparative Example 6 is a wet-laid synthetic paper,and Comparative Example 7 is the wet-laid synthetic paper of Example 6plus a 20 g/m² meltblown fiber layer. The example results are shown inTable I below. When Example 2 is compared to composites in ComparativeExamples 4, 5, and 7 efficiency is not sacrificed at the expense ofreducing resistance which yields the associated high Quality Factorvalues.

TABLE I Basis Weight Efficiency Resistance Quality Example (g/m²) (%)(mm H₂O) Factor Example 1 158.6 57.0 1.78 525 Spunbond PolyesterBicomponent Fiber Base Example 2 154.6 80.2 3.43 534 Spunbond PolyesterBicomponent Fiber Base + 2 gm² Nanofiber Layer Comparative Example 3234.9 28.7 9.3 40 Drylaid Polyester Base Comparative Example 4 236.343.2 13.81 45 Drylaid Polyester Base + 2 g/m² Nanofiber LayerComparative Example 5 121.2 40.5 9.77 59 Wet laid Synthetic Paper + <0.5g/m² Nanofiber Layer Comparative Example 6 133.4 9.0 7.67 14 WetlaidSynthetic Paper Comparative Example 7 150.2 86.4 8.79 251 WetlaidSynthetic Paper + 20 g/m² Meltblown Fiber LayerEfficiency measured at 0.3 microns, 5.3 cm/s face velocity (ASHRAE52.2-1999). Resistance measured in accordance with EN-1822 (1998).

Quality Factor defined by the equation:

Q _(f)=−25000·log(P/100)/Δp

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

1. A method of making a composite filter media, said method comprising:forming a nonwoven fabric mat comprising a plurality of synthetic fibersby a spunbond process; calendaring the nonwoven fabric mat withembossing calendar rolls to form a bond area pattern comprising aplurality of substantially parallel discontinuous lines of bond area tobond the synthetic fibers together to form a nonwoven fabric, thenonwoven fabric having a minimum filtration efficiency of about 50%,measured in accordance with ASHRAE 52.2-1999 test procedure; andapplying a nanofiber layer by electro-blown spinning a polymer solutionto form a plurality of nanofibers on at least one side of the nonwovenfabric to form the composite filter media, the composite filter mediahaving a minimum filtration efficiency of about 75%, measured inaccordance with ASHRAE 52.2-1999 test procedure.
 2. A method inaccordance with claim 1, wherein the nonwoven fabric and the nanofiberlayer in combination are substantially electrically neutral.
 3. A methodin accordance with claim 1, wherein forming a nonwoven fabric matcomprising a plurality of synthetic fibers by a spunbond processcomprises forming a nonwoven fabric mat comprising a plurality ofsynthetic bicomponent fibers by a spunbond process, the plurality ofbicomponent fibers comprising a core material and a sheath material, thesheath material having a lower melting point than the core material. 4.A method in accordance with claim 1, wherein applying a nanofiber layercomprises applying a nanofiber layer by an electro-blown spinningprocess, an electrospinning process, a centrifugal spinning process, ora melt blowing process.
 5. A method in accordance with claim 3, whereinthe core material comprises at least one of polyester, polyamide,polyolefin, thermoplastic polyurethane, polyetherimide, polyphenylether, polyphenylene sulfide, polysulfone, and aramid.
 6. A method inaccordance with claim 1, wherein calendaring the nonwoven fabric matcomprises calendaring the nonwoven fabric mat from a nonwoven fabrichaving a basis weight of about 100 g/m² to about 300 g/m².
 7. A methodin accordance with claim 1, wherein calendaring the nonwoven fabric matcomprises calendaring the nonwoven fabric mat form a nonwoven fabrichaving a basis weight of about 150 g/m² to about 220 g/m².
 8. A methodin accordance with claim 1, wherein applying a nanofiber layer comprisesapplying a plurality of nanofibers having an average diameter of about500 nm or less to form the nanofiber layer having a basis weight ofabout 0.6 g/m² to about 20 g/m².
 9. A method in accordance with claim 1,wherein applying a nanofiber layer comprises applying a plurality ofnanofibers having an average diameter of about 500 nm or less to formthe nanofiber layer having a basis weight of about 1.5 g/m² to about 2.5g/m².
 10. A method in accordance with claim 1, wherein calendaring thenonwoven fabric mat with embossing calendar rolls to form a bond areapattern comprises calendaring the nonwoven fabric mat with embossingcalendar rolls to form a bond area pattern having a bond area of thespunbond fibers of about 10% to about 16% of an area of the nonwovenfabric.
 11. A method in accordance with claim 3, wherein forming anonwoven fabric mat comprising a plurality of synthetic fibers by aspunbond process comprises forming a nonwoven fabric mat comprising aplurality of synthetic bicomponent fibers having an average diameter ofabout 12 to about 25 microns.
 12. A method in accordance with claim 1,wherein the nonwoven fabric has a resistance less than about 2.5 mm ofwater, measured in accordance with EN-1822 (1998), and the compositefilter media has a resistance less than about 4.0 mm of water, measuredin accordance with EN-1822 (1998).
 13. A method in accordance with claim12, wherein a quality factor Q_(f) of the composite filter media isgreater than about
 450. 14. A method in accordance with claim 12,wherein a quality factor Q_(f) of the composite filter media is greaterthan about
 500. 15. A method in accordance with claim 1, wherein thenanofiber layer comprises a plurality of nanofibers, the nanofibersformed from polymers utilizing the electro-blown spinning process, thepolymers comprising at least one of polyimides, polyamides,polyaramides, polybenzimidazoles, polyetherimides, polyacrylonitriles,polyethylene terephthalate, polypropylene, polyanilines, polyethyleneoxides, polyethylene naphthalates, polybutylene terephthalate, styrenebutadiene rubber, polystyrene, polyvinyl chloride, polyvinyl alcohol,polyvinylidene chloride, polyvinyl butylenes, and copolymer orderivative compounds thereof.
 16. A method in accordance with claim 1,further comprising pleating the composite filter media.